Enhanced Loading of Proteins Into Hydrogel Delivery Vehicles

Hydrogels are widely used as vehicles for the controlled release of therapeutic proteins because of their ability to control the location and rate of release of a protein to the body.  In most cases, cross-linked gels must be formed prior to loading with the protein to avoid side reactions with the protein, or inability to remove unreacted byproducts without also leaching out the protein.  Loading of macromolecules into pre-formed gels, however, can be limited by the phenomenon of size exclusion.  However, we have shown that entropic size exclusion of proteins from polymer networks can be overcome using the thermodynamic principles of aqueous two phase extraction.  This concept, typically used for protein purification, uses the fact that solutions of two water soluble polymers typically split into two immiscible phases, and that proteins partition unevenly between these phases.  Using dextran and poly(ethylene glycol) diacrylate (PEGDA) gels, we have shown that by adding a thermodynamically incompatible polymer to the loading solution in which a gel is immersed, the protein partition coefficient into the gel can be increased over two orders of magnitude, and loading over 20 wt% (dry basis) protein can be achieved by this simple method.